Science and technology

Obesity and health

Fat years

BEING fat is bad for you. That, at least, is the received wisdom. In reality the picture is more complex, because the prevailing measure of fatness, weight in kilograms divided by height in metres squared, known as the body-mass index (BMI), is imperfect and because bad for you is a vague term. According to a new study in the Journal of the American Medical Association (JAMA), being a bit too pudgy may in fact reduce the risk of dying in a given period.

Researchers, led by Katherine Flegal of Americas Centres for Disease Control and Prevention, examined nearly 100 studies of more than 2.9m people and 270,000 deaths. Being overweight is defined as having a BMI between 25 and 30. People with a BMI of 30 or more are considered obese. Dr Flegal and her colleagues observed that obesity was associated with a higher risk of mortality in a given study period. Interestingly, those who were only moderately obese (with a BMI of 30-35) had a 5% lower risk of death than those of normal weight and those who were merely overweight had a 6% lower risk. The mortality risk was much higher for those with BMI of 35 or above—they had a 29% higher risk of death in a given period than those of normal weight.

Dr Flegal included studies of general populations, not just those in hospital or with specific conditions. But her findings add new fuel to the debate over what is called the obesity paradox. Those with chronic diseases such as diabetes and heart conditions seem to show an inverse relationship between BMI and mortality—that is, being moderately overweight seems to have a protective effect.

Just why this is true remains unclear. It may be because the overweight receive life-prolonging medical care, such as treatment for diabetes and drugs to control heart conditions. It may be that they are better equipped to endure surgery. Among those who sought angioplasty for coronary artery disease, a higher BMI was linked with a higher rate of survival. Or, as Wolfram Doehner argued in 2010, chronic illness—of any sort, not just that linked to obesity—may be a metabolically demanding state, with the overweight having more energy reserves to meet that demand. Most controversially, Peter Unger and Philipp Scherer have suggested that body fat may in fact be not the cause of the bundle of conditions associated with obesity, like heart and liver disease, stroke and late-onset diabetes, but its consequence. The body may use fat tissue to mop up excess lipids caused by overeating. These chemicals, which include fats, are needed in small amounts to make cell membranes. But when fat tissue becomes overloaded, the hypothesis goes, those lipids wreak havoc on other parts of the body. More body fat therefore constitutes a useful buffer.

Whatever the explanation, the latest research highlights three important points. First, physicians must think carefully about diet advice for those who already have chronic conditions. Second, the study is yet another reminder that BMI is a poor measure of health. It just about works as a rough gauge of obesity, but does not account for sex, race, age or fitness. And BMI says nothing about the distribution of fat in the body. Another study in JAMA, published in September, suggested that BMI was not independently linked with diabetes. Fat storage in the lower body even seemed to protect against disease. Visceral fat, packed around the organs, seems to be the most harmful.

Third, the study may bolster the already strong case (see our special report) for governments to prevent even moderate obesity. Relatively plump citizens may indeed pose a particular burden on the state. On the one hand, they run a higher risk than those who are less fat of developing chronic ailments such as heart disease and diabetes that require expensive treatment. On the other, corpulence may extend life, meaning such treatment may be needed for many extra years. Expanding waistlines could be making people live longer, but sicker.

This article really botched the reasons why the epidemiology from this study must be taken with a grain of salt!
1. The study included "underweight" people in the normal "non overweight" category. This is a massive problem because often people who are underweight have chronic diseases like cancer or lung diseases. This pretty much makes the whole study pointless.
2. BMI is a poor tool for comparing "normal weight" to "over weight (but not obese)" because many people who exercise end up building muscle and bone density, which bumps them up into the "over weigh but not obese" category.

Sure - as long as those people who want to "weigh whatever they damn well feel they should weigh" won't spend more tax money than an average person, for diseases they inflicted upon themselves. Unfortunately, they do - and it's unfair to use my tax money for their lack of individual responsibility.

Both of them found:
"The lowest all-cause mortality was generally observed in the BMI range of 20.0 to 24.9" Berrington de Gonzalez

"In the cohorts of East Asians, including Chinese, Japanese, and Koreans, the lowest risk of death was seen among persons with a BMI (the weight in kilograms divided by the square of the height in meters) in the range of 22.6 to 27.5." Zheng

Flegal study clumped people from multiple genetic backgrounds (Zheng stude i.e has shown that Indians behaved differently, see below) and included as normal weight 18.5-25, which nominally correct, but hides higher mortality rates for ppl with BMI < 20. Hell, even the JAMA editorial accompanying the Flegal article stated something along the lines:
"""
Finally, for them, the lack of excess risk of mortality among overweight individuals is an artifact related to the fact that mixing a wide range of BMI in the "normal" weight. They suggest that the results would have been different if the stratification was different, especially if BMI between 18.5 and 22 and 22 and 25 were separated.
(translated from: http://www.theheart.org/fr/article/1493165.do)
"""

Zhang:
"""
As with the findings for death from any cause, a U-shaped association was seen between BMI and the risk of death from cardiovascular disease, cancer, or other causes among East Asians but not among Indians and Bangladeshis (Figure 1Figure 1Association between Body-Mass Index and Risk of Cause-Specific Death in Two Asian Populations.). In fact, no elevated risk of death from any of these three causes was seen in the high-BMI groups of Indians and Bangladeshis.
"""

TLDR: there are multiple studies of this type, and picking up Flegal and not looking at others does not allow to see the outlier. Flegal study looks like one.

"Third, the study may bolster the already strong case (see our special report) for governments to prevent even moderate obesity."

The state also has a strong interest in keeping people productive until the age of about 60, then shooting them in the head, to avoid all of those costs associated with old age. In a free society, however, the state is discouraged from doing so, because the state is there to serve the citizenry, not visa versa. The same reasoning applied to weight would encourage the state to let people weigh whatever they damn well feel they should weigh.

I'm 6'2, and I weigh 220 lbs... everyone thinks I have athletic type body, but according to BMI, I'm just about OBESE.. not just overweight, but obese.

So, when I hear people start to spout how other people's weight is now a government issue. I just think... if governments use such flawed measures as BMI, then we are all in for tyranny by arbitrary technocrats. And the reality is that any population-level measurement is going to be flawed on an individual basis.

I hope that readers view this new "research" with the same amount of skepticism that others from the political right appeared to hold out on research on the climate. I am afraid they will not, however. Unfortunately, when a scientist says there may be global warming, they are questioned and their research is attacked, with the assumption the research is faulty and probably politically motivated. However, when a scientist claims that their data shows that being a bit obese may lead to a longer life, people basically take that as fact and then simply consider the ramifications; never minding the quality of the research or the possible political motivations.

Although I have never seen a scientific study of average years lived vs body weight, I do know that every single person I have ever seen who has lived to be over 90 has always been thin; no exception. After noticing this I have a asked a few freinds, and they have confirmed the same thing. So I wonder how exactly they are measuring 'live longer, but sicker', it would be nice to see a better discussion of data within this article to better understand the exact nature of this observed trend.

Harvesting data from previously published research is called meta-analysis. It is valuable, as in this case, because it allows for huge sample pools (e.g., 2.9 million people, 270,000 deaths). Denouncing all meta-analyses is "the birtherism of science."

I think if you examine bmi stats from before 1980 +/-, you will see that 20 would be sort of normal. Today, 25 has become normal. The airlines have added about 25 pounds per passenger to estimate the weight of the plane at takeoff. Were we all malnourished back in the '60s or just not couch potatoes?

I think passing 90 makes you an outlier. Life expectancy is lower than 90 in the USA. What is interesting to me is how life expectancy changes with age. A person who lives to 90 may have more "Time" left than the average person at 80 because the sick 80 year olds don't make it to 90. In general life expectancy increases with age as you are less likely to do foolish things....

It has been my experience too that people over 90 are rarely fat. So added weight helps in the short run, but also limits your end point.

Hi Idler...People at TE comment all the time on a very important issue: how stories are being covered in the media as we are talking about a story that is being covered by one of the publications in the media, namely, TE. Moreover, this publication and others that are covering this story have also in the past regularly covered "new scientific evidence" as it pertains to other issues such as smoking, natural gas exploration or even climate change, with some valuable lessons learned of how it is viewed, how it is being reported on, and yes, how people agree with or debunk the rearch reported on.

Since the entire analysis is based on using BMI to assess the health of individuals, it's fundamentally flawed from the start. BMI is a statistical measure to assess the weight of an entire population and has no validity on an individual level. It tends to significantly overstate obesity because it can't account for an individual's body type or genetics. So it could just be that these people weren't actually obese anyway, which kind of makes the whole thing pointless.